Now. Open Rulesmd.ini and go to the [FV] entry.
Unless you've modified it, you should see this tag:
TurretCount=4
This controls the amount of turrets your IFV unit will have. For the purposes of this tutorial, we are going to set this to 13. There is an upward limit of 15 on this, if you add more than 15 turrets, the >15th turrets will not display correctly, if at all.
Now, the IFV turret logic is highly underused, there are only ever 4 turrets used: the missile turret, the repair arm, the machine gun, and the 'high-tech' turret as the rulesmd terms it. There are more contained in local.mix, but these are mostly unfinished.
The IFV Turret Pack contains 13 different turrets.
We are going to leave three of the four turrets in the game (the high-tech one will be replaced).

Now, you can either copy and paste the files I'm about to list, then rename them, or just rename them now, whichever you prefer.
Rename the voxels from the filenames on the left, to the filenames on the right:
fvtur_flak2 - fvtur3
fvtur_sealgun - fvtur4
fvtur_sniper1 - fvtur5
fvtur_tesla - fvtur6
fvtur_nuke - fvtur7
fvtur_chaos - fvtur8
fvtur_radbeam - fvtur9
fvtur_rail - fvtur10
fvtur_sniper2 - fvtur11
fvtur_dualmiss - fvtur12

Now using XCC MIX Editor, place those in an expandmdxx.mix file (xx = integer between 10 and 99) and place that in the RA2 directory.